Carbocyanine dyes and method of preparing them



Patented Nov. 7, 1933 1334,55?

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CARBOCYANINE DYES AND METHOD OF PREPARING THEM Leslie G. S. Brooker,Rochester, N. Y., assignor to Eastman Kodak Company, Rochester, N. Y., acorporation of New York No Drawing. Application March 5, 1931 Serial No.520,459

19 Claims. (Cl. 260-44) This invention relates to a new composition Ihave found that dyes having good photoof matter, and particularly to anew class of sensitizingv properties may be prepared by the photographicsensitizing dyes, and a method for treatment of a l-methylbenzothiazolealkyl their preparation. quaternary salt with an ortho-ester of an ali-As ordinary photographic emulsions are genphatic carboxylic acid, theacid corresponding erally indifferent to those colors of the spectrum towhich contains more than two carbon atoms of longer wave lengths,various types of sensitizin the molecule. The reaction may be carrieding dyes have been suggested for incorporaout in boiling dry pyridine.The ortho-esters tion in photographic emulsions, or for employof thecarboxylic acids which I have found pa 1.) ing over emulsions asovercoatings so as to inticularly suitable include such esters astrimethyl 0 crease the spectral sensitiveness thereof. Many orthopropionate, methyldiethyl ortho-ncyanine dyes have been described forthis purcaproate, methyldiethyl ortho-isocaproate, and

pose containing the benzothiazole nucleus, trimethyl ortho-valerate. I

whilst classes of these photo-sensitizing dyes The reaction of al-methylbenzothiazole containing the naphthothiazole nucleus are dealkylquarternary salt with one ofthese ortho- 5 scribed in my co-pendingapplications of Serial esters of a carboxylic acid in the presence ofNo. 337,177 filed February 2, 1929; Nos. 435,104 pyridine may be writtengraphically as follows:

6 s 6 p 5 5 +2ROH+R 0H+ 4 4 3 A /g/ \N A 30 7 and 435,105, filed March12, 1930; and No. 437,- In the above structures R represents an alkyl017, filed March 19, 1930, whilst those containgroup and X an acidradical. A stands for the ing the thiazoline nucleus are described in myalkyl group to be introduced into the three-carco-pending applicationSerial No. 460,548 filed bon chain of the thiocarbocyanine dye and OR 35June 11, 1930 and those containing the thiazole and OR. represent thealkoxy groupings of the 35 nucleus are described in my co-pendingapplicaortho-ester and these may be similar or dissimition Ser. No.548,026 filed June 30, 1931. lar. The dye molecule is numbered as shown,so

An object of the present invention is to provide that a compound of thistype may be described a process for the preparation of photo-sensitizasa 2:2'-dialkyl-8-alkyl-thiocarbocyanine salt.

10 ing dyes of the thiocarbocyanine series contain- In the'actualpractice it is frequently desirable ing benzothiazole nuclei and havingalkyl subto carry out the condensation with an acid radical stituentswith more than one carbon atom in such as the p toluenesulfonate, whichconfers a the radical attached to the central carbon atom comparativelyhigh degree of solubility on the 1- of the three-carbon chain.methylbenzothiazole alkyl quaternary salt and on 45 A further object ofthis invention is to pmthe dye. The latter is then conveniently isolatedvide such photo-sensitizing dyes as may be added as a less soluble saltby double-decomposition in to photographic emulsions or coated thereonas the ordinary way, such salts as ammonium or an overcoating wherebythe spectral. sensitivity potassium bromide or iodide being employed forof the photographic emulsion is increased. this purpose, usually inaqueous solution.

5 Other objects will hereinafter appear. The CH: groupv is called themethenyl group and therefore the chain CI-I=CHCI- may be called atri-methenyl chain, and the chain may similarly be called a tri-methenylchain in which the hydrogen attached to the central carbon atom has beenreplaced by the group denoted by the letter A.

The nomenclature and numbering of the above classes of compounds andintermediates are in accord with present usage and also the system usedin my co-pending applications given above. The numbering, of course, isarbitrary and is given for the guidance of those skilled in the art inorder that there be no question as to the identity of acompound coveredby my invention.

The methods for the formation of the 1- methylbenzothiazoles (used inthe preparation of the photographic sensitizing dyes herein described)are given in the literature. One general method consists of theconversion of the acetyl compound of an aromatic primary amine, such asp.toluidine, into the thio-acetyl compound by the action of phosphorouspentasulfide. This thio-acetyl compound is then dissolved in aqueouscaustic alkali solution and oxidized with a cold aqueous solution ofalkali ferricyanide whereupon the base is produced and may be extractedwith ether.

The preparation of some of the ortho-esters of the aliphthaticcarboxylic acids, the acids corresponding to which have more than twocarbon atoms in the molecule have not, however, been described in theliterature and I will give here, therefore, one method for theirpreparation. These ortho-esters are prepared by taking the nitrile ofthe corresponding acid as the starting material. The nitrile (one mol.)is dissolved in dry absolute ethyl ether together with an alcohol (1mol.) such as methyl or ethyl alcohol, all of the reactants being asfree from moisture as possible, and dry hydrochloric acid gas (rathermore than 1 mol.) is led in, using good cooling throughout theoperation. The imino-ether hydrochloride separates "and'the whole iskept cold until crystallization appears to be complete, when thecrystals are filtered ofi, carefully washed with dry absolute ethylether and dried in a vacuum over solid caustic potash until free fromall excess 7 of hydrochloric acid. The dry imino-ether hydrochloride isthen decomposed at room temperature with an alcohol, taking rougly 2 cc.of the alcohol, as free from moisture as possible, for every gram of thehydrochloride. The latter dissolves more or less completely and theformation of the ortho-ester is accompanied by the separation ofammonium chloride, the formation of which may be used as an indicationof the course of the reaction.

The reaction vessel is tightly stoppered and allowed to stand forseveral days or even several weeks until the reaction is apparentlycomplete. The insoluble material is then filtered off and the excessalcohol is removed by distillation, filtering again if necessary. Theester is finally distilled over, using diminished pressure as a rule,and is purified by refractionation. Thus propionitrile on treatment withmethyl alcohol and hydrochloric acid gas in the manner described aboveyields propio-imino-methyl-ether hydrochloride, and this, when subjectedto the action of methyl alcohol in the manner described, yieldstrimethyl ortho-propionate. Mixed esters may be made by taking twodifierent alcohols for the two separate steps of the reaction. Thusn-capronitrile may be converted into n-capro-iminomethyl-etherhydrochloride by the joint action of methyl alcohol and hydrochloricacid gas and this on further treatment with ethyl alcohol yieldsmethyldiethyl ortho-n-caproate as the principal product. Theortho-esters of other aliphatic carboxylic acids having more than twocarbon atoms in the molecule may be prepared in a similar manner.

I will now give several examples for preparing various dyes referred to,but it will be understood that they are merely representative of a greatnumber of reactions in which the proportions given and equivalents usedmay vary in accord with the particular type of dye required. Myinvention, therefore, will not be restricted there by except asindicated in the appended claims.

The l-methylbenzothiazole used in any of the described condensations maybe unsubstituted in the benzene nucleus, or it may be substitutedtherein, as for example by a fused-on benzene nucleus, as described inmy co-pending application Serial No. 435,104.

EXAMPLE 1 2:2: 8-triethyithiocarbocyanine iodide 6.1 g. (1 mol.) ofl-methylbenzothiazole ethiodide was refluxed for one hour with 5.4 g. (2mols., 300% excess) trimethyl ortho-propionate and 30 cc. dry pyridine.The solution was welldiluted with water and let stand for several daysto crystallize out. Greenish-bronze crystals were obtained, weighing 0.6g., which were crystallized from a mixture of acetone and methylalcohol. Dark green prisms separated showing a bronze reflex and thesolution was bluish-red.

A larger yield of the material was obtained as follows. '7 g. (1 mol.)of l-methylbenzothiazole etho-p-toluene-sulfonate was/boiled underreflux for one hour with 2.7 g. (1 mol.) trimethyl ortho-propionate and7 cc. dry pyridine. A warm solution of 10 g. potassium iodide in 50 cc.water was added and the iodide of the dye was filtered off when cold andobtained as a dull greenishblack powder weighing 3.67 g. after washingwith water and with cold acetone. This was crystallized from 50 cc.methyl alcohol using an extraction apparatus and on cooling the dyecrystallized out in beautiful prisms, some faces of which reflected bluelight and others green light.

If in place of the l-methylbenzothiazole ethop-toluene-sulfonate usedabove. one employs 6.7 g. (1 mol.) of l-methylbenzothiazolemethop-toluenesulfonate (made by condensing equimolecular proportions oflnethylbenzothiazole and methyl-p-toluenesulfonate together overnight onthe steam bath and crystallizing the crude salt from ethyl alcohol anddrying it well) and refluxes it for an hour with 2.7 g. (1 mol.) oftrimethyl ortho-propionate and 20 cc. pyridine, 2:2di1nethyl-8-ethylthiocarbocyanine ptoluenesulfonate will be produced.The dye may beisolated as the bromide by precipitating it with an excessof an aqueous solution of ammonium bromide and weighed 2.9 g. when dry.The dye crystallizes from methyl alcohol in purplish-brown needles witha green reflex, and gives a bluish-red solution in this solvent.

EXAMPLE 2 8-ethyZ-2: 2'-diailylthiocarbocyanine iodide 12.7 g. (1 mol.)of l-methylbenzothiazole alliodide (made by condensing the base with anequivalent amount of allyl iodide and purifying EXAMPLE 3 5 :v 5-dimethyZ-2 2 8-triethylthiocarbocya'nine iodide 4.1 g. (1 mol.)1:5-dimethylbenzothiazole was heated overnight in an oil bath at 140-150C. with 5.5 g. (1.1 mol.) ethyl p-toluene-sulfonate. The crudequaternary salt was then refluxed for forty-five minutes with 4.4 g. (1mol.) triethyl ortho-propionate and 20 cc. dry pyridine. A solution or"20 g. potassium iodide in 100 cc. hot

7 water was used to precipitate the dye as the iodide, and after themixture had cooled, the dye was filtered off and washed, and 3.4 g. of adark green crystalline powder was obtained on drying. The dye wascrystallized from methyl alcohol, dark green crystals being obtainedwhich gave a bluish-red solution in this solvent.

- EXAMPLE 4 2: 2-dimethyl-8-n-butylthiocarbocyanine iodide 6.7 g. (1mol.) of l-methylbenzothiazole methop-toluene-sulfonate wasrefiuxed-withfifi g. (2 mols.) trimethyl ortho-n-valerate (obtained fromn-valeronitrile) and 15 cc. dry pyridine for forty minutes. The dye wasprecipitated as the iodide using 10 g. of potassium iodide dissolved in50 cc. of hot water, when a felted mass of crystals was obtained whichwei hed 3.1 g. after filtering, washing and drying. When recrystallizedfrom methyl alcohol the dye formeddark purplish needles with agreenish-blue reflex. The solution of the dye in methyl alcohol wasbluish-red.

EXAMPLE 5 2: 2-dethyl8-n-butylthiocarbocyanine iodide "7.0 g. (1 mol.)l-methylbenzothiazole ethop-toluene-sulfonate was refluxed with 6.5 g.(2 mols.) of trimethyl ortho-n-valerate and 20 cc. dry pyridine forforty minutes. The dye was precipitated as the iodide using .a solutionof 20 g. potassium iodide in 100 cc. hot water, when rapidcrystallization occurred. The dye weighed 3.8 g. after filtering,washing and drying, and when recrystallized from methyl alcohol formedbeautiful greenish-gray crystals, with a marcasite-like lustre, whichgave a bluish-red solution in the solvent.

EXAMPLE 6 2: 2-dimeth1/Z-8-namylthiocarbocyanine iodide 6.7 g. (1 mol.)l-methylbenzothiazole methop-toluene-sulfonate was refluxed for an hourwith 8.2 g. (2 mols.) of methyl-diethyl ortho-n-caproate (obtained fromn-capronitrile) and '30 cc. dry pyridine. The dye was then precipitatedas the iodide using a solution of 10 g. potassium iodide in 50 cc. hotwater for this purpose. The product crystallized on cooling and wasfiltered also be apparent tha off, washed, and dried. Weight 3.4 g.Reddish needles with a brilliant blue reflex were obtained onrecrystallizing the dye from methyl alcohol, the solution beingbluish-red.

. EXAMPLE '7 2: 2 diethyZ-?n-amylthiocarbocyanine iodide 7.0g. (1 mol.)l-niethylbenzothiazole etho-ptoluene-sulionate was refluxed for about anhour with 3.2 g. (2 mols.) methyldiethyl ortho n-caproate and 15 cc. drypyridine. The reaction mixture was then treated with a solution of 10 g.potassium iodide dissolved in 50 cc. of hot water and the whole allowedto stand overnight. The product, when filtered, washed with waterfollowed by acetone, and dried, weighed 35 g. The dye crystallized frommethyl alcohol in greenishbronze granular crystals and gave a bluish-redsolution.

EXAMPLE 8 '95 2: 2'-diethyZ-8-n-amyithiocarbocyanine iodide 6.7 g. (1mol.) l-rnethylbenzothiazole methop-toluene-sulfonate was refluxed with8.2 g. (2 mols.) methyldiethyl ortho-isocaproate (obtained fromisocapronitrile) and 20 cc. pyridine for forty m'nutes. The dye wasprecipitated as the iodide, using a solution of 10 g. potassium iodidein 50 cc. hot water and weighed 1.8 g. when filtered off, washed, anddried. It crystallized from methyl alcohol in compact dark bluish-greyprisms with a green reflex, and gave a bluish-red solution in thissolvent.

By substituting various alkyl groups having more than one carbon atom inthe position in the structural formula of .the dye occupied by theletter A, and various alkyl groups in the two positions occupied by theletter R, many sensitizing dyes may be obtained. The letter X indicatesany suitable anion such, for example, as a halide, p-toluenesulionate,alkylosulphate, nitrate, acetate, perchlorate, or, in fact, any saltforming anion that will not render the dye too sparingly soluble ordeleteriously affect the photographic sensitizing properties of the dye.

It is apparent from a thorough consideration of the above descriptionthat any thiocarbocyanine dye prepared from a l-methylbenzothiazoleunsubstituted or substituted, in which the 8 position of the dye issubstituted by an alkyl group containing more than one carbon atom, willcome within the scope of this invention whatever may be the radicalsoccupying the other substitutable positions of the structure.Furthermore, it will i the genus claimed hereinafter not only includesthe foregoing but also includes any carbocyanine dye containing two ofthe five-membered rings linked together by a tri-methenyl chain, the hy-In the claims, by an ortho-ester of an aliphatic carboxylic acid ismeant an ortho-ester of a carboxylic acid, the acid corresponding towhich contains a simple, unsubstituted alkyl group directly attached tothe carbon atom of the carboxyl group. Examples of such ortho estershave already been given.

While the principal use now known for these new chemical compounds isfor sensitizing photographic emulsions it may well be that other usestherefor will be discovered from time to time and consequently it is notintended that the foregoing description of the sensitizing properties ofthese dyes shall in any way limit the scope of the claims appendedhereto. The combination of the dyes with a photographic emulsion isclaimed in my co-pending application Serial No. 505,982 filed December31, 1930.

What I claim as my invention and desire to be secured by Letters Patentof the United States is:

1. A carbocyanine dye of the following structure in which each D equalsan ethylene, vinylene, phenylene or naphthylene group, R equals an alkylradical, X equals an acid radical and A equals an alkyl radicalcontaining more than one carbon atom.

2. A thiocarbocyanine dye of the following structure in which D equals aphenylene group, R equals an alkyl radical, X equals an acid radical andA equals an alkyl radical containing more than one carbon atom.

3. A thiocarbocyanine salt substituted in the 8 position with an alkylradical containing more than one carbon atom.

4. A 2:2'-dialky1-8-alkylthiocarbocyanine salt in which the S-alkylgroup contains more than one carbon atom.

5. A 5:5 -dimethyl-2 :2 -8-triethy1thiocarbocyanine salt.

6. A 2 2 -dimethyl-8-n-butylthiocarbocyanine salt.

7. A 2:2-dimethyl 8- ethylthiocarbocyanine salt.

8. A 2:2-dia1kyl-8-alkylthiocarbocyanine halide in which the 8-alkylgroup contains more than one carbon atom.

9. 5:5'-dimethyl-2:2 8 triethylthiocarbocyanine iodide.

10. 2':2'-dimethy1-8n butylthiocarbocyanine iodide,

11. 2:2 dimethyl 8 ethylthiocarbocyanine bromide.

12. The process of preparing carbocyanine dyes which comprisescondensing, under the influence of heat, one molecular proportion of anorthoester of an aliphatic monocarboxylic acid, the acid correspondingto which contains more than two carbon atoms, with two molecularproportions of a compound having the structure in which D equals anethylene, vinylene, phenylene or naphthylene group, R equals an alkylradical and X equals an acid radical.

13. The process of preparing carbocyanine dyes which comprisescondensing, under the influence of heat, two molecular proportions of anonmethyl-benzothiazole quaternary salt with one molecular proportion ofan ortho-ester of an aliphatic monobasic carboxylic acid, the acidcorresponding to which contains more than two carbon atoms.

14. The process of preparing carbocyanine dyes which comprisescondensing, under the influence of heat, a l-methylbenzothiazole alkylquaternary salt with a trialkyl ortho-ester of an aliphatic monobasiccarboxylic acid, the acid corresponding to which contains more than twocarbon atoms in the molecule.

15. The process of preparing carbocyanine dyes which comprisescondensing, under the influence of heat, a l-methylbenzothiazole alkylquaternary salt with a trialkyl ortho-n-valerate;

16. The process of preparing carbocyanine dyes which comprisescondensing, under the influence of heat, a l-methylbenzothiazole alkylquaternary salt with a trialkyl ortho-propionate.

17. The process of preparing carbocyanine dyes which comprisescondensing, under the influence of heat, a l-methylbenzothiazolealkyl-p-toluenesulfonate with a trialkyl ortho-ester of an aliphaticmonobasic carboxylic acid, the acid corresponding to which contains morethan two carbon atoms in the molecule.

18. The process of preparing carbocyanine dyes which comprisescondensing, under the influence of heat, a l-nethylbenzothiazolealkyl-p-toluenesulfonate with a trialkyl ortho-n-valerate.

19. The process of preparing carbocyanine dyes which comprisescondensing, under the influence of heat, a l-methylbenzothiazolealkyl-p-toluene sulfonate witha trialkyl ortho-propionate.

LESLIE G. S. BROOKER.

